1. Technical Field
The present invention relates generally to a rotary drill for use in drilling. More particularly, the present invention relates to an earth drilling apparatus having extendable cutting blades for cutting or underreaming.
2. Summary of Related Art
Well drilling operations frequently require that the area being drilled be expanded at selected points. In many instances, where a pipe casing or lining is in place, the pipe requires clearing of debris or other material from deep inside the well. In each of these situations a special type of drill known as an underreamer is required.
Underreaming drills allow for the widening of a selected area in a well. In general, an underreaming drill includes a pilot bit portion and an underreaming tool attached upstream from the pilot bit portion. The underreaming tool includes plurality of cutting blades that are movable as a group between a retracted position and an extended position. In their retracted position, the blades are folded into the body of the underreaming tool, thus allowing insertion and extraction of the tool from the area being worked. In their extended position, the blades are pivoted to a position which is substantially perpendicular to the long axis of the tool. While extended, the blades are able to underream an area thus enlarging the region for a given purpose.
While the general object of blade retraction and extension has been achieved by many tools, movement of the blades has been effected by a variety of mechanisms. For example, underreamers which include rack-and-pinion like gear and driver arrangements are disclosed in U.S. Pat. No. 5,402,856 issued to Warren et al. on Apr. 4, 1995, for ANTI-WHIRL UNDERREAMER, U.S. Pat. No. 3,208,540 issued to Park on Sep. 28, 1965, for EXPANSIBLE ROTARY WELL DRILLING BIT, U.S. Pat. No. 2,872,160 issued to Barg on Feb. 3, 1959, for HYDRAULIC EXPANSIBLE ROTARY WELL DRILLING BIT, and U.S. Pat. No. 1,478,306 issued to Sweetman on Dec. 18, 1923, for UNDERREAMER. In general, in each of these patents one set of teeth are formed on a curved end-surface of each blade, while another set of teeth are formed on an axially-movable driver assembly. The blades are pivotably attached to the hollow drill body.
U.S. Pat. No. 4,431,065 issued to Andrews on Feb. 14, 1984, for UNDERREAMER and U.S. Pat. No. 5,010,955 issued to Springer on Apr. 30, 1991, for CASING MILL AND METHOD teach a gear arrangement similar to the patents mentioned immediately above, but further include a stop arrangement for halting the outward pivoting of the blades. While such a stop is arguably inherent in the patents mentioned immediately above, the arrangement is more positively defined in these latter patents.
Additional variations may be seen in U.S. Pat. No. 4,116,012, issued to Abe et al. on Sep. 26, 1978, for METHOD OF OBTAINING SUFFICIENT SUPPORTING FORCE FOR A CONCRETE PILE SUNK INTO A HOLE, U.S. Pat. No. 3,548,362, issued to Blank, Jr. on Dec. 15, 1970, for WELL CASING CONTACT TOOL, U.S. Pat. No. 2,756,968, issued to Emanuel et al. on Jul. 31, 1956, for EXPANSIBLE WELL SCRAPER, U.S. Pat. No. 2,124,663, issued to Wintemute on Jul. 26, 1938, for ROTARY UNDERREAMER, and U.S. Pat. No. 1,667,155 issued to Higdon on Apr. 24, 1928, for DRILLING BIT, which teach various arrangements of slots alone or slots and driving pins which are engaged to selectively effect outward or inward pivoting movement of cutting blades with respect to the drill shaft for underreaming.
While arguable providing improvements in the art of underreamer drills, the art still suffers from a variety of problems. The environment in which these drills operate causes frequent problems to the underreaming assembly, such as debris entanglement and premature wear. The prior art mechanisms, while perhaps well-engineered, are overly complex and require for too much xe2x80x9cdown timexe2x80x9d for the tool and, hence, the drilling operation. Disassembly and reassembly are difficult and time consuming. Hours are lost when a tool fails and has to be withdrawn, repaired and reinserted.
By way of example, cutting blades of known underreamers are pivotably retained to the assembly by set-screw arrangements. High rotational speed and hard materials frequently cause these screws to break, thus allowing parts of the tool to drop into the well, requiring removal of the tool and an extensive fishing expedition to recover the dropped parts. The heads of the set screws themselves, being externally exposed, are subject to wear, further complicating disassembly and reassembly.
In addition, known drilling apparatus frequently suffer from premature wear on not only the drilling assembly but also on the connection between the cutting blades and the body of the underreamer due to the tortional force being concentrated at the connection where the cutting blades are extended.
Accordingly, a simple yet effective underreaming apparatus remains wanting.
It is the general object of the present invention to provide an underreaming assembly to overcome the problems of the prior art.
More particularly, it is an object of the present invention to provide an underreaming apparatus which is relatively easy to operate and which provides for minimal operational xe2x80x9cdown time.xe2x80x9d
It is a further object of the present invention to provide such an apparatus which may be readily disassembled and reassembled for changing the cutting blades.
Still an additional object of the present invention is to provide such an apparatus which has a minimal number of parts and threaded elements.
A further object is to provide a dynamic fluid chamber that is able to axially drive a mandrel on the build-up of a selected fluid pressure to effect extension of the cutting blades, thereby providing an efficient and positive engagement mechanism.
An additional object of the present invention is to provide such an apparatus which is capable of transferring torque to the entire underreaming when the cutting blades are extended.
These and other objects are accomplished by the provision of a drilling apparatus having extendable cutting blades for cutting or underreaming. The drilling apparatus of the present invention includes a top sub, a pressure sleeve mated to the top sub, and a blade body mated to the pressure sleeve. A pilot bit is mated to the lower end of the blade body. A plurality of movable cutting blades are pivotably attached to the blade body by pivot pins. Each of the pins is inserted through the blade body and the cutting blade. Slidable covers, held in place by the pressure sleeve, are used to retain the pins. A mandrel is centrally positioned with respect to the pressure sleeve and the blade body and is axially movable therein. Each of the cutting blades includes an end which is operatively associated with channels transversely formed on one end of the mandrel.
Movement of the mandrel in a first axial direction effects retraction of the cutting blades. Movement of the mandrel in a second axial direction effects extension of the cutting blades. The mandrel is held in its blade-retracting position by the biasing force of a spring. A build-up of hydraulic fluid, selectively delivered from the operator, in a pressure chamber formed between the pressure sleeve and the mandrel causes the mandrel to be moved to its blade-extending position when a critical mass of fluid pressure is achieved.